Molecular Humification Mechanisms of Dissolved Organic Matter during Maize Straw Composting Enhanced by Humus Soil Biomaterial: Paired-Molecule Mass Difference Reactomics Analysis Based on FT-ICR MS

This study investigated molecular humification mechanisms of dissolved organic matter during maize straw composting enhanced by humus soil biomaterial using paired-molecule mass difference reactomics analysis and high-throughput sequencing. Results indicated that the composting process predominantly involved three molecular humification pathways, namely, the phenol-protein reaction, polyphenol self-condensation, and Maillard reaction, with N-containing molecules showing the highest reactivity. Proteins were hydrolyzed into N-containing intermediates in the initial composting stage, which rapidly polymerized with phenol from humus soil biomaterial to form humic acids, improving organic nitrogen retention. Lignin was decomposed and oxidized into phenolics and quinones mainly during the middle and later composting stages, which either self-condensed or polymerized with protein derivatives to assemble humic acids. Concurrently, some amino acids and monosaccharides underwent the Maillard reaction to produce humic acids. Furthermore, humus soil biomaterial introduced the genus Alicyclobacillus into the composting system, contributing to microbial community stability. This work provides valuable molecular insights into the maize straw composting humification process and promotes the sustainable utilization of agricultural waste in soil.